Method of producing a multilayer body by coalescence and the multi-layer body produced

ABSTRACT

A method of producing a multilayer body by coalescence, characterised in that the method comprises the steps of a) filling, a pre-compacting mould with a start material in the form of powder, pellets, grains and the like, b) pre-compacting the start material at least once and c) compressing the material in a compression mould by at least one stroke, where a striking unit emits enough kinetic energy to form the body when striking the material inserted in the compression mould, causing coalescence of the material, d) at least one further material being inserted into the mould in the form of powder, pellets, grains and the like, either in step a), after compacting in step b) or after compressing the first material in step c), e) if necessary, further pre-compacting and/or compressing being performed after the insertion of the at least one further material.

[0001] The invention concerns a method of producing a multilayer body bycoalescence as well as the multilayer body produced by this method.

STATE OF THE ART

[0002] In WO-A1-9700751, an impact machine and a method of cutting rodswith the machine is described. The document also describes a method ofdeforming a metal body. The method utilises the machine described in thedocument and is characterised in that a metallic material either insolid form or in the form of powder such as grains, pellets and thelike, is fixed preferably at the end of a mould, holder or the like andthat the material is subjected to adiabatic coalescence by a strikingunit such as an impact ram, the motion of the ram being effected by aliquid. The machine is thoroughly described in the WO document.

[0003] In WO-A1-9700751, shaping of components, such as spheres, isdescribed. A metal powder is supplied to a tool divided in two parts,and the powder is supplied through a connecting tube. The metal powderhas preferably been gas-atomized. A rod passing through the connectingtube is subjected to impact from the percussion machine in order toinfluence the material enclosed in the spherical mould. However, it isnot shown in any embodiment specifing parameters for how a body isproduced according to this method.

[0004] The compacting according to this document is performed in severalsteps, e.g. three. These steps are performed very quickly and the threestrokes are performed as described below.

[0005] Stroke 1: an extremely light stroke, which forces out most of theair from the powder and orients the powder particles to ensure thatthere are no great irregularities.

[0006] Stroke 2: a stroke with very high energy density and high impactvelocity, for local adiabatic coalescence of the powder particles sothat they are compressed against each other to extremely high density.The local temperature increase of each particle is dependent on thedegree of deformation during the stroke.

[0007] Stroke 3: a stroke with medium-high energy and with high contactenergy for final shaping of the substantially compact material body. Thecompacted body can thereafter be sintered.

[0008] In SE 9803956-3 a method and a device for deformation of amaterial body are described. This is substantially a development of theinvention described in WO-A1-9700751. In the method according to theSwedish application, the striking unit is brought to the material bysuch a velocity that at least one rebounding blow of the striking unitis generated, wherein the rebounding blow is counteracted whereby atleast one further stroke of the striking unit is generated.

[0009] The strokes according to the method in the WO document, give alocally very high temperature increase in the material, which can leadto phase changes in the material during the heating or cooling. Whenusing the counteracting of the rebounding blows and when at least onefurther stroke is generated, this stroke contributes to the wave goingback and forth and being generated by the kinetic energy of the firststroke, proceeding during a longer period. This leads to furtherdeformation of the material and with a lower impulse than would havebeen necessary without the counteracting. It has now shown that themachine according to these mentioned documents does not work so well.For example are the time intervals between the strokes, which theymention, not possible to obtain. Further, the document does not compriseany embodiments showing that a body can be formed.

OBJECT OF THE INVENTION

[0010] The object of the present invention is to achieve a process forefficient production of multilayer products at a low cost. Theseproducts may be both medical devices such as medical implants or bonecement in orthopaedic surgery, instruments or diagnostic equipment, ornon medical devices such as tools, insulator applications, crucibles,spray nozzles, tubes, cutting edges, jointing rings, ball bearings andengine parts. Another object is to achieve a multilayer product of thedescribed type.

[0011] The term multilayer is used here to define a product composed ofdifferent parts integrally joined to each other. These parts may be inthe form of flat layers or have any other suitable form provided thatthe form of the different parts fit closely together. One part may havea convex surface fitting around a concave surface on another part.Examples of different multilayer products are shown in FIGS. 2a-2 f. Thedifferent parts may be made of the same type of material or of differenttypes of material. It is possible to combine a ceramic material with alayer of a polymeric material. It is also possible to have a multilayerproduct with layers or parts of different polymers.

[0012] It should also be possible to perform the new process at a muchlower velocity than the processes described in the above documents.Further, the process should not be limited to using the above describedmachine.

SHORT DESCRIPTION OF THE INVENTION

[0013] It has surprisingly been found that it is possible to compressdifferent multilayer products according to the new method defined inclaim 1. The material to be compressed is for example in the form ofpowder, pellets, grains and the like and is filled in a mould,pre-compacted and compressed by at least one stroke. The machine to usein the method may be the one described in WO-A1-9700751 and SE9803956-3.

[0014] The method according to the invention utilises hydraulics in thepercussion machine, which may be the machine utilised in WO-A1-9700751and SE 9803956-3. When using pure hydraulic means in the machine, thestriking unit can be given such movement that, upon impact with thematerial to be compressed, it emits sufficient energy at sufficientspeed for coalescence to be achieved. This coalescence may be adiabatic.A stroke is carried out quickly and for some materials the wave in thematerial decay in between 5 and 15 milliseconds. The hydraulic use alsogives a better sequence control and lower running costs compared to theuse of compressed air. A spring-actuated percussion machine will be morecomplicated to use and will give rise to long setting times and poorflexibility when integrating it with other machines. The methodaccording to the invention will thus be less expensive and easier tocarry out. The optimal machine has a large press for pre-compacting andpost-compacting and a small striking unit with high speed. Machinesaccording to such a construction are therefore probably more interestingto use. Different machines could also be used, one for thepre-compacting and post-compacting and one for the compression.

SHORT DESCRIPTION OF THE DRAWINGS

[0015] On the enclosed drawings

[0016]FIG. 1 shows a cross sectional view of a device for deformation ofa material in the form of a powder, pellets, grains and the like,

[0017]FIGS. 2a-2 f shows the forming of different types of multilayerproducts and

[0018] FIGS. 3-4 are diagrams showing results obtained in theembodiments described in the examples.

DETAILED DESCRIPTION OF THE INVENTION

[0019] The invention concerns a method of producing a multilayer body bycoalescence, wherein the method comprises the steps of

[0020] a) filling a pre-compacting mould with a start material in theform of powder, pellets, grains and the like,

[0021] b) pre-compacting the material at least once and

[0022] c) compressing the material in a compression mould by at leastone stroke, where a striking unit emits enough kinetic energy to formthe body when striking the material inserted in the compression mould,causing coalescence of the material,

[0023] d) at least one further material being inserted into the mould inthe form of powder, pellets, grains and the like, either in step a),after compacting in step b) or after compressing the start material instep c),

[0024] e) if necessary, further pre-compacting and/or compressing beingperformed after the insertion of the at least one further material.

[0025] The pre-compacting mould may be the same as the compressionmould, which means that the material does not have to be moved betweenthe step b) and c). It is also possible to use different moulds and movethe material between the steps b) and c) from the pre-compacting mouldto the compression mould. This could only be done if a body is formed ofthe material in the pre-compacting step.

[0026] According to one embodiment the first material is onlypre-compacted before the insertion of the second material. Thereafter, asecond pre-compaction is performed and the multilayer material is struckwith at least one stroke to achieve coalescence and form an integralproduct. It is also possible to insert the further material or materialsin powder form before the pre-compaction or the first or start material.All materials will be compacted and struck together in this case.

[0027] According to another embodiment the first and second materialsare inserted in powder form beside each other or as layers above eachother, whereafter pre-compaction and striking are performed.

[0028] According to a third embodiment the first material ispre-compacted and struck to make a coalescent element, whereafter thiselement is placed in a second mould on top of a powder of the secondmaterial or surrounded by the second material. The first elementtogether with the second material are pre-compacted and struck with acoalescing stroke.

[0029] In the description below any step described may refer to aprocess performed on one layer or element of the multilayer product oron several layers or elements together.

[0030] The device in FIG. 1 comprises a striking unit 2. The material inFIG. 1 is in the form of powder, pellets, grains or the like. The deviceis arranged with a striking unit 3, which with a powerful impact mayachieve an immediate and relatively large deformation of the materialbody 1. The invention also refers to compression of a body, which willbe described below. In such a case, a solid body 1, such as a solidhomogeneous multilayer body, would be placed in a mould.

[0031] The striking unit 2 is so arranged, that, under influence of thegravitation force, which acts thereon, it accelerates against thematerial 1. The mass m of the striking unit 2 is preferably essentiallylarger than the mass of the material 1. By that, the need of a highimpact velocity of the striking unit 2 can be reduced somewhat. Thestriking unit 2 is allowed to hit the material 1, and the striking unit2 emits enough kinetic energy to compress and form the body whenstriking the material in the compression mould. This causes a localcoalescence and thereby a consequent deformation of the material 1 isachieved. The deformation of the material 1 is plastic and consequentlypermanent. Waves or vibrations are generated in the material 1 in thedirection of the impact direction of the striking unit 2. These waves orvibrations have high kinetic energy and will activate slip planes in thematerial and also cause relative displacement of the grains of thepowder. It is possible that the coalescence may be an adiabaticcoalescence. The local increase in temperature develops spot welding(inter-particular melting) in the material which increases the density.

[0032] The pre-compaction is a very important step. This is done inorder to drive out air and orient the particles in the material. Thepre-compaction step is much slower than the compression step, andtherefore it is easier to drive out the air. The compression step, whichis done very quickly, may not have the same possibility to drive outair. In such case, the air may be enclosed in the produced body, whichis a disadvantage. The pre-compaction is performed at a minimum pressureenough to obtain a maximum degree of packing of the particles whichresults in a maximum contact surface between the particles. This ismaterial dependent and depends on the softness and melting point of thematerial.

[0033] The pre-compacting step in the Examples has been performed bycompacting with an axial load of about 117680 N. This is done in thepre-compacting mould or the final mould. According to the examples inthis description, this has been done in a cylindrical mould, which is apart of the tool, and has a circular cross section with a diameter of 30mm, and the area of this cross section is about 7 cm². This means that apressure of about 1.7×10⁸ N/m² has been used. For hydroxyapatite thematerial may be pre-compacted with a pressure of at least about 0.25×10⁸N/m², and preferably with a pressure of at least about 0.6×10⁸ N/m². Thenecessary or preferred pre-compaction pressure to be used is materialdependent and for a softer multilayer it could be enough to compact at apressure of about 0.2×10⁸ N/m². Other possible values are 1.0×10⁸ N/m²,1.5×10⁸ N/m². The studies made in this application are made in air andat room temperature. All values obtained in the studies are thusachieved in air and room temperature. It may be possible to use lowerpressures if vacuum or heated material is used. The height of thecylinder is 60 mm. In the claims is referred to a striking area and thisarea is the area of the circular cross section of the striking unitwhich acts on the material in the mould. The striking area in this caseis the cross section area.

[0034] In the claims it is also referred to the cylindrical mould usedin the Examples. In this mould the area of the striking area and thearea of the cross section of the cylindrical mould are the same.However, other constructions of the moulds could be used, such as aspherical mould. In such a mould, the striking area would be less thanthe cross section of the spherical mould.

[0035] The invention further comprises a method of producing amultilayer body by coalescence, wherein the method comprises compressinga solid body of a first or start material (i.e. a body where the targetdensity for specific applications has been achieved) together with atleast one further material in the form of powder or in the form of asolid body in a compression mould by at least one stroke, where astriking unit emits enough energy to cause coalescence of the materialin the body. Slip planes are activated during a large local temperatureincrease in the material, whereby the deformation is achieved. Themethod also comprises deforming the body.

[0036] The method according to the invention could be described in thefollowing way. 1) Powder is pressed to a green body, the body iscompressed by impact to a (semi)solid body and thereafter an energyretention may be achieved in the body by a post-compacting. The process,which could be described as Dynamic Forging Impact Energy Retention(DFIER) involves three mains steps.

[0037] a)Pressuring

[0038] The pressing step is very much like cold and hot pressing. Theintention is to get a green body from powder. It has turned out to bemost beneficial to perform two compactions of the powder. One compactionalone gives about 2-3% lower density than two consecutive compactions ofthe powder. This step is the preparation of the powder by evacuation ofthe air and orientation of the powder particles in a beneficial way. Thedensity values of the green body is more or less the same as for normalcold and hot pressuring.

[0039] b)Impact

[0040] The impact step is the actual high-speed step, where a strikingunit strikes the powder with a defined area. A material wave starts offin the powder and interparticular melting takes place between the powderparticles. Velocity of the striking unit seems to have an important roleonly during a very short time initially. The mass of the powder and theproperties of the material decides the extent of the interparticularmelting taking place.

[0041] c)Energy Retention

[0042] d)

[0043] The energy retention step aims at keeping the delivered energyinside the solid body produced. It is physically a compaction with atleast the same pressure as the pre-compaction of the powder. The resultis an increase of the density of the produced body by about 1-2%. It isperformed by letting the striking unit stay in place on the solid bodyafter the impact and press with at least the same pressure as atpre-compaction, or release after the impact step. The idea is that moretransformations of the powder will take place in the produced body.

[0044] According to the method, the compression strokes emit a totalenergy corresponding to at least 100 Nm in a cylindrical tool having astriking area of 7 cm² in air and at room temperature. Other totalenergy levels may be at least 300, 600, 1000, 1500, 2000, 2500, 3000 and3500 Nm. Energy levels of at least 10 000, 20 000 Nm may also be used.There is a new machine, which has the capacity to strike with 60 000 Nmin one stroke. Of course such high values may also be used. And ifseveral such strikes are used, the total amount of energy may reachseveral 100 000 Nm. The energy levels depend on the material used, andin which application the body produced will be used. Different energylevels for one material will give different relative densities of thematerial body. The higher energy level, the more dense material will beobtained. Different materials will need different energy levels to getthe same density. This depends on for example the hardness of thematerial and the melting point of the material.

[0045] According to the method, the compression strokes emit an energyper mass corresponding to at least 5 Nm/g in a cylindrical tool having astriking area of 7 cm² in air and at room temperature. Other energiesper mass may be at least 20 Nm/g, 50 Nm/g, 100 Nm/g, 150 Nm/g, 200 Nm/g,250 Nm/g, 350 Nm/g and 450 Nm/g.

[0046] There may be a linear relationship between the mass of the sampleand the energy needed to achieve a certain relative density. However,for some materials the relative density may be a function of the totalimpact energy.

[0047] These values will vary dependent on what material is used. Aperson skilled in the art will be able to test at what values the massdependency will be valid and when there may be a mass independence.

[0048] The energy level needs to be amended and adapted to the form andconstruction of the mould. If for example, the mould is spherical,another energy level will be needed. A person skilled in the art will beable to test what energy level is needed with a special form, with thehelp and direction of the values given above. The energy level dependson what the body will be used for, i.e. which relative density isdesired, the geometry of the mould and the properties of the material.The striking unit must emit enough kinetic energy to form a body whenstriking the material inserted in the compression mould. With a highervelocity of the stroke, more vibrations, increased friction betweenparticles,. increased local heat, and increased interparticular meltingof the material will be achieved. The bigger the stroke area is, themore vibrations are achieved. There is a limit where more energy will bedelivered to the tool than to the material. Therefore, there is also anoptimum for the height of the material.

[0049] When powders for a multilayer product are inserted in a mould andthe materials are struck by a striking unit, a coalescence is achievedin the powder material and the material will float. A probableexplanation is that the coalescence in the material arises from wavesbeing generated back and forth at the moment when the striking unitrebounds from the material body or the material in the mould. Thesewaves give rise to a kinetic energy in the material body. Due to thetransmitted energy a local increase in temperature occurs, and enablesthe particles to soften, deform and the surface of the particles willmelt. The inter-particular melting enables the particles to re-solidifytogether and dense material can be obtained. This also affects thesmoothness of the body surface. The more a material is compressed by thecoalescence technique, the smoother surface is obtained. The porosity ofthe material and the surface is also affected by the method. If a poroussurface or body is desired, the material should not be compressed asmuch as if a less porous surface or body is desired.

[0050] The individual strokes affect material orientation, driving outair, pre-moulding, coalescence, tool filling and final calibration. Ithas been noted that the back and forth going waves travels essentiallyin the stroke direction of the striking unit, i. e. from the surface ofthe material body which is hit by the striking unit to the surface whichis placed against the bottom of the mould and then back.

[0051] What has been described above about the energy transformation andwave generation also refer to a solid body. In the present invention asolid body is a body where the target density for specific applicationshas been achieved.

[0052] The striking unit preferably has a velocity of at least 0.1 m/sor at least 1.5 m/s during the stroke in order to give the impact therequired energy level. Much lower velocities may be used than accordingto the technique in the prior art. The velocity depends on the weight ofthe striking unit and what energy is desired. The total energy level inthe compression step is at least about 100 to 4000 Nm. But much higherenergy levels may be used. By total energy is meant the energy level forall strokes added together. The striking unit makes at least one strokeor a number of consecutive strokes. The interval between the strokesaccording to the Examples was 0.4 and 0.8 seconds. For example at leasttwo strikes may be used. According to the Examples one stroke has shownpromising results. These Examples were performed in air and at roomtemperature. If for example vacuum and heat or some other improvingtreating is used, perhaps even lower energies may be used to obtain goodrelative densities.

[0053] The multilayer product may be compressed to a relative density of60%, preferably 65%. More preferred relative densities are also 70% and75%. Other preferred densities are 80 and 85%. Densities of at least 90and up to 100% are especially preferred. However, other relativedensities are also possible. If a green body is to be produced, it maybe enough with a relative density of about 40-60%. Load bearing implantsneed a relative density of 90 to 100% and in some biomaterials it isgood with some porosity. If a porosity of at most 5% is obtained andthis is sufficient for the use, no further post-processing is necessary.This may be the choice for certain applications. If a relative densityof less than 95% is obtained, and this is not enough, the process needto continue with further processing such as sintering. Severalmanufacturing steps have even in this case been cut compared toconventional manufacturing methods.

[0054] The method also comprises pre-compacting the material at leasttwice. It has been shown that this could be advantageous in order to geta high relative density compared to strokes used with the same totalenergy and only one pre-compacting. Two compactions may give about 1-5%higher density than one compacting depending on the material used. Theincrease may be even higher for some materials. When pre-compactingtwice, the compacting steps are performed with a small interval between,such as about 5 seconds. About the same pressure may be used in thesecond pre-compacting.

[0055] Further, the method may also comprise a step of compacting thematerial at least once after the compression step. This has also beenshown to give very good results. The post-compacting should be carriedout at at least the same pressure as the pre-compacting pressure, i.e.0,25×10⁸ N/m². Other possible values are 1.0×10⁸ N/m². Higherpost-compacting pressures may also be desired, such as a pressure whichis twice the pressure of the pre-compacting pressure. For hydroxyapatitethe pre-compacting pressure should be at least about 0.25×10⁸ N/m² andthis would be the lowest possible post-compacting pressure forhydroxyapatite. The pre-compacting value has to be tested out for everymaterial. A post-compacting effects the sample differently than apre-compacting. The transmitted energy, which increases the localtemperature between the powder particles from the stroke, is conservedfor a longer time and can effect the sample to consolidate for a longerperiod after the stroke. The energy is kept inside the solid bodyproduced. Probably the “lifetime” for the material wave in the sampleincreases and it can affect the sample for a longer period and moreparticles can melt together. The after compaction or post-compaction isperformed by letting the striking unit stay in place on the solid bodyafter the impact and press with at least the same pressure as atpre-compacting, i.e. at least about 0.25×10⁸ N/m² hydroxyapatite. Moretransformations of the powder will take place in the produced body. Theresult is an increase of the density of the produced body by about 1-4%.Also this possible increase is material dependent. When usingpre-compacting and/or after compacting, it could be possible to uselighter strokes and higher pre- and/or after compacting, which wouldlead to saving of the tools, since lower energy levels could be used.This depends on the intended use and what material is used. It couldalso be a way to get a higher relative density.

[0056] To get improved relative density it is also possible topre-process the material before the process. The powder could bepre-heated to e.g. ˜200-300° C. or higher depending on what materialtype to pre-heat. The powder could be pre-heated to a temperature whichis close to the melting temperature of the material. Suitable ways ofpre-heating may be used, such as normal heating of the powder in anoven. In order to get a more dense material during the pre-compactingstep vacuum or inert gas could be used. This would have the effect thatair is not enclosed in the material to the same extent during theprocess.

[0057] The body may according to another embodiment of the invention beheated and/or sintered any time after compression or post-compacting. Apost-heating is used to relax the bindings in the material (obtained byincreased binding strain). A lower sintering temperature may be usedowing to the fact that the compacted body has a higher density thancompacts obtained by other types of powder compression. This is anadvantage as a higher temperature may cause decomposition ortransformation of the constituting material. The produced body may alsobe post-processed in some other way, such as by HIP (Hot IsostaticPressing).

[0058] Further, the body produced may be a green body and the method mayalso comprise a further step of sintering the green body. The green bodyof the invention gives a coherent integral body even without use of anyadditives. Thus, the green body may be stored and handled and alsoworked, for instance polished or cut. It may also be possible to use thegreen body as a finished product, without any intervening sintering.This is the case when the body is a bone implant or replacement wherethe implant is to be resorbed in the bone.

[0059] Before processing the materials for the multilayer product couldbe homogenously mixed with additives. Predrying of the granulate couldalso be used to decrease the water content of the raw material. Somemultilayers do not absorb humidity, while other multilayers easilyabsorb humidity which can disturb the processing of the material, anddecrease the homogeneity of the worked material because a high humidityrate can raise steam bubbles in the material.

[0060] The multilayer materials may be chosen from the group comprisinga metallic, polymeric or ceramic materials such as stainless steel,aluminium alloy, titanium, UHMWPE, PMMA, PEEK, rubber, alumina,zirconia, silicon carbide, hydroxyapatite or silicon nitride. Themultilayer may comprise a composite material containing reinforcementsfibres or powders from the group comprising carbon, metals, glass orceramics such as alumina, silica, silicon nitride, zirconia, siliconcarbide.

[0061] The compression strokes need to emit a total energy correspondingto at least 100 Nm in a cylindrical tool having a striking area of 7 cm²for multilayer products or layers. The compression strokes need to emitan energy per mass corresponding to at least 5 Nm/g in a cylindricaltool having a striking area of 7 cm² for multilayer products.

[0062] It has been shown earlier that better results have been obtainedwith particles having irregular particle morphology. The particle sizedistribution should probably be wide. Small particles could fill up theempty space between big particles.

[0063] The first or second material may comprise a lubricant and/or asintering aid. A lubricant may be useful to mix with the material.Sometimes the material needs a lubricant in the mould, in order toeasily remove the body. In certain cases this could be a choice if alubricant is used in the material, since this also makes it easier toremove the body from the mould.

[0064] A lubricant cools, takes up space and lubricates the materialparticles. This is both negative and positive.

[0065] Interior lubrication is good, because the particles will thenslip in place more easily and thereby compact the body to a higherdegree. It is good for pure compaction. Interior lubrication decreasesthe friction between the particles, thereby emitting less energy, andthe result is less inter-particular melting. It is not good forcompression to achieve a high density, and the lubricant must be removedfor example with sintering.

[0066] Exterior lubrication increases the amount of energy delivered tothe material and thereby indirectly diminishes the load on the tool. Theresult is more vibrations in the material, increased energy and agreater degree of inter-particular melting. Less material sticks to themould and the body is easier to extrude. It is good for both compactionand compression.

[0067] An example of a lubricant is Acrawax C, but other conventionallubricants may be used. If the material will be used in a medical body,the lubricant need to be medically acceptable, or it should be removedin some way during the process.

[0068] Polishing and cleaning of the tool may be avoided if the tool islubricated and if the powder is preheated.

[0069] A sintering aid may also be included in the material. Thesintering aid may be useful in a later processing step, such as asintering step. However, the sintering aid is in some cases not souseful during the method embodiment, which does not include a sinteringstep. The sintering aid may be yttrium oxide, alumina or magnesia orsome other conventional sintering aid. It should, as the lubricant, alsobe medically acceptable or removed, if used in a medical body.

[0070] In some cases, it may be useful to use both a lubricant and asintering aid. This depends on the process used, the material used andthe intended use of the body which is produced.

[0071] In some cases it may be necessary to use a lubricant in the mouldin order to remove the body easily. It is also possible to use a coatingin the mould. The coating may be made of for example TiNAl or BalinitHardlube. If the tool has an optimal coating no material will stick tothe tool parts and consume part of the delivered energy, which increasethe energy delivered to the powder. No time-consuming lubricating wouldbe necessary in cases where it is difficult to remove the formed body.

[0072] A very dense material, and depending on the material, a hardmaterial will be achieved, when the multilayer material is produced bycoalescence. The surface of the material will be very smooth, which isimportant in several applications.

[0073] If several strokes are used, they may be executed continually orvarious intervals may be inserted between the strokes, thereby offeringwide variation with regard to the strokes.

[0074] For example, one to about six strokes may be used. The energylevel could be the same for all strokes, the energy could be increasingor decreasing. Stroke series may start with at least two strokes withthe same level and the last stroke has the double energy. The oppositecould also be used.

[0075] The highest density is often obtained by delivering a totalenergy with one stroke. If the total energy instead is delivered byseveral strokes a lower relative density may be obtained, but the toolis saved. A multi-stroke can therefore be used for applications where amaximum relative density is not necessary.

[0076] Through a series of quick impacts a material body is suppliedcontinually with kinetic energy which contributes to keep the back andforth going wave alive. This supports generation of further deformationof the material at the same time as a new impact generates a furtherplastic, permanent deformation of the material.

[0077] According to another embodiment of the invention, the impulse,with which the striking unit hits the material body, decreases for eachstroke in a series of strokes. Preferably the difference is largebetween the first and second stroke. It will also be easier to achieve asecond stroke with smaller impulse than the first impulse during such ashort period (preferably approximately 1 ms), for example by aneffective reduction of the rebounding blow. It is however possible toapply a larger impulse than the first or preceding stroke, if required.

[0078] According to the invention, many variants of impacting arepossible to use. It is not necessary to use the counteracting of thestriking unit in order to use a smaller impulse in the followingstrokes. Other variations may be used, for example where the impulse isincreasing in following strokes, or only one stroke with a high or lowimpact. Several different series of impacts may be used, with differenttime intervals between the impacts.

[0079] A multilayer body produced by the method of the invention, may beused in medical devices such as medical implants or bone cement inorthopaedic surgery, instruments or diagnostic equipment. Such implantsmay be for examples skeletal or tooth prostheses.

[0080] According to an embodiment of the invention, the material ismedically acceptable. Such materials are for example suitable multilayerproducts containing an element or layer of hydroxyapatite or zirconia.

[0081] A material to be used in implants needs to be biocompatible andhaemocoinpatible as well as mechanically durable, such as hydroxyapatiteand zirconia or other suitable multilayer materials.

[0082] The body produced by the process of the present invention mayalso be a non medical product such as cutting tools, insulatorapplications, crucibles, spray nozzles, tubes, cutting edges, jointingrings, ball bearings and engine parts.

[0083] Here follows several applications for some of the materials whichmay be used in the present multilayer products. Applications for siliconnitride are crucibles, spray nozzles, tubes, cutting edges, jointingrings, ball bearings and engine parts. Alumina is a good electricalinsulator and has at the same time an acceptable thermal conductivityand is therefore used for producing substrates where electricalcomponents are mounted, insulation for ignition plugs and insulation inthe high-tension areas. Alumina is also a common material type inorthopaedic implants, e.g. femoral-head in hip prostheses.Hydroxyapatite is one of the most important biomaterials extensivelyused in orthopaedic surgery. Common applications for zirconia arecutting tools, components for adiabatic engines and it is also a commonmaterial type in orthopaedic implants, e.g. femoral-head in hipprostheses. The invention thus has a big application area for producingproducts according to the invention.

[0084] When the material inserted in the mould is exposed to thecoalescence, a hard, smooth and dense surface is achieved on the bodyformed. This is an important feature of the body. A hard surface givesthe body excellent mechanical properties such as high abrasionresistance and scratch resistance. The smooth and dense surface makesthe material resistant to for example corrosion. The less pores, thelarger strength is obtained in the product; This refers to both openpores and the total amount of pores. In conventional methods, a goal isto reduce the amount of open pores, since open pores are not possible toget reduced by sintering.

[0085] It is important to admix powder mixtures until they are ashomogeneous as possible in order to obtain a body having optimumproperties.

[0086] A coating may also be manufactured according to the method of theinvention. A coating may for example be formed on a surface of anelement or of a multilayer product. When manufacturing a coated element,the element is placed in the mould and may be fixed therein in aconventional way. The coating material is inserted in the mould aroundthe element to be coated, by for example gas-atomizing, and thereafterthe coating is formed by coalescence. The element to be coated may beany material formed according to this application, or it may be anyconventionally formed element. Such a coating may be very advantageous,since the coating can give the element specific properties.

[0087] A coating may also be applied on a body produced in accordancewith the invention in a conventional way, such as by dip coating andspray coating.

[0088] It is also possible to first compress a material in a first mouldby at least one stroke. Thereafter the material may be moved to another,larger mould and a further material be inserted in the mould, whichmaterial is thereafter compressed on top of or on the sides of the firstcompressed material, by at least one stroke. Many different combinationsare possible, in the choice of the energy of the strokes and in thechoice of materials.

[0089] The invention also concerns the product obtained by the methodsdescribed above.

[0090] The method according to the invention has several advantagescompared to pressing. Pressing methods comprise a first step of forminga green body from a powder containing sinterinc, aids. This green bodywill be sintered in a second step, wherein the sintering aids are burnedout or may be burned out in a further step. The pressing methods alsorequire a final working of the body produced, since the surface need tobe mechanically worked. According to the method of the invention, it ispossible to produce the body in one step or two steps and no mechanicalworking of the surface of the body is needed.

[0091] By the use of the present process it is possible to produce largebodies in one piece. In presently used processes it is often necessaryto produce the intended body in several pieces to be joined togetherbefore use. The pieces may for example be joined using screws oradhesives or a combination thereof.

[0092] A further advantage is that the method of the invention may beused on powder carrying a charge repelling the particles withouttreating the powder to neutralize the charge. The process may beperformed independent of the electrical charges or surface tensions ofthe powder particles. However, this does not exclude a possible use of afurther powder or additive carrying an opposite charge. By the use ofthe present method it is possible to control the surface tension of thebody produced. In some instances a low surface tension may be desired,such as for a wearing surface requiring a liquid film, in otherinstances a high surface tension is desired.

[0093] Here follow some Examples to illustrate the invention.

EXAMPLES

[0094] The following material were tested: Silicone nitride,hydroxyapatite, Alumina, titanium, Co-28Cr-6Mo, PMMA and UHMWPE.

[0095] Silicone nitride was a pure freeze granulated powder.Hydroxyapatite and alumina was not pre-processed at all. The metal andpolymer powder was initially dry-mixed for 10 minutes to obtain ahomogeneous particle size distribution in the powder.

[0096] A multilayer has many applications areas e.g. implants.

[0097] Six different multi layers was tested with different materialcombination.

[0098] 2Two horizontal layers

[0099] 3Three horizontal layers

[0100] 1.One horizontal and two vertical layers

[0101] 2.Two vertical layers

[0102] 3.Two horizontal layers and two vertical layers

[0103] 4.Four vertical layers.

[0104] The main goal was to evaluate the possibility to obtain solidlayers bonded to each other with chemical bonding.

[0105] The weight specified in the test specification of eachconstituent of the multilayer was divided by the number of layers in themultilayer. This means that the impact energy to obtain a visibilityindex for the weight specified in the test specification also has to bedivided by the number of layers. If a horizontal layer consisted of twovertical layers then the material with the lowest hardness has to beconsider when choosing impact energies. A polymer was never processedlike material 1 as a single horizontal layer.

[0106] Following test scheme was general for all different layers:

[0107] 1Pre-compacting procedure for layer 1

[0108] 1.1Pre-compacting by hand

[0109] 1.2Pre-compacting with the striking unit, 12000 kp axial load.

[0110] 2Impact energy levels for layer 1 before adding material 2

[0111] 2.1Strike with an energy corresponding to visibility index 1

[0112] 2.2Strike with an energy corresponding to visibility index 2

[0113] 2.3Strike with an energy corresponding to visibility index 3

[0114] 3The multilayer impact stroke will be performed with machinepre-compacting and the maximum allowable impact energy for material 2and 3 respectively. Depending if the multilayer has two or threehorizontal layers.

[0115] A approximately theoretical density was calculated for thedifferent multilayer by dividing the total mass of the three layers withthe sum of each material mass divided by the materials specifictheoretical density,ρ_(multilayer)=m_(total)/(m_(a)/ρ_(a)+m_(b)/ρ_(b)+m_(c)/r_(d)+m_(c)/ρ_(d)+.m_(c)/ρ_(d))

[0116] After each layer the over die was removed and next powder waspoured and processed. When the multilayer was complete then the toolparts were dismounted and the sample was released. The diameter andthickness were measured with electronic micrometers which rendered thevolume of the body. Thereafter the weight was electronicallyestablished. Out of these results the density 1 was obtained by takingthe weight divided by the volume.

[0117] To be able to continue with the next sample, the tool needed tobe cleaned, either or only with acetone or polishing the tool surfaceswith an emery cloth to get rid of the material rests on the tool.

[0118] Table 1 shows the different powders used in this study. TABLE 1Silicone Properties nitride Hydroxyapatite Alumina Co-28Cr-6Mo TitaniumPMMA UHMWPE Particle size <0.5 <1 <0.5 <150 <150 <600 (micron) Particle— <1 0.3-0.5 2% > 150 −5% <250 distribution balance < 150   5%  25-355(micron)   10% 355-500   45% 500-710   35% <710 Particle Cubic Irregularirregular Irregular Irregular Irregular morphology Powder Granulated Wetchemistry Grinding Water atomised Hydrided ex-reacted productionprecipitation Crystal structure 98% alfa Apatite alfa 85% alpha phase,HCP amorphous 2% beta 15% carbides (hexagonal) Theoretical 3.18 3.153.98 8.5 4.5 1.19 density (g/cm³) Apparent density 0.38 0.6 0.5-0.8 3.41.8 — (g/cm³) Melting 1800 1600 2050 1350-1450 1660 125° C. temperature(° C.) Sintering 1820 900 1600-1650 1200 1000 — temperature (° C.)Particle hardnes 1570 450 1770 460-830 60 M92-100 (HB)

[0119] Two Horizontal Layers

[0120]FIG. 2a shows the look of a two horizontal layer. The differentmaterial combinations used are specified in table 2.

[0121] There were no solid samples obtained after compressinghydroxyapatite and UHMWPE together. The hydroxyapatite could be solidbefore adding the polymer but then it cracked when the polymer was addedand struck. Compressing hydroxyapatite and titanium gave a similarresult for the hydroxyapatite. The titanium became a solid body afterpre-compacting with the machine but when the titanium as material 2 wasstruck it cracked the hydroxyapatite. The best result was obtained byhandcompacting the hydroxyapatite and then add the titanium powder.

[0122] Alumina and silicone nitride has not been successfully compressedas a single material and the same result was obtained in the multilayercompressing series. The ceramic material felled apart and could not bindto the added material 2.

[0123] Compressing titanium together with UHMWPE or PMMA gave solidsamples when the titanium first was struck to a solid body and then thepolymer was struck. The polymer had to melt and get plastic to bond tothe titanium. If the titanium only were hand compacted the polymerseemed still to be powder.

[0124] Co-28Cr-6Mo has also been complicated to solidified as a singlematerial. It was compressed together with PMMA and UHMWPE. Some solidsamples were obtained with UHMWPE when Co-28Cr-6Mo was struck to a solidmaterial body first. No fine samples for the Co-28Cr-6Mo/PMMA two-layerwere obtained. TABLE 2 Number of Material 1 Material 2 samplesHydroxyapatite UHMWPE 2 Hydroxyapatite Titanium 6 Alumina UHMWPE 8Titanium PMMA 7 Titanium UHMWPE 5 Co-28Cr-6Mo PMMA 8 Co-28Cr-6Mo UHMWPE9 Silicone nitride Titanium 5 Silicone nitride UHMWPE 5

[0125] Three Horizontal Layers

[0126]FIG. 2b shows the look of a three horizontal layer. The differentmaterial combinations used are specified in table 3.

[0127] It was difficult to obtain solid sample when three layers werecompressed together. Often was the single layer solid but there was noobtained mechanical or chemical bonding between the layers. The bestresults were obtained when both the first and second material where onlyhand compacted or pre-compacted with the machine and then struck with ahigh impact energy. It seemed to be a mechanical bonding between thelayers and the material body was solid.

[0128] Table 3 shows the different material combinations tested in threehorizontal layers. TABLE 3 Number of Material 1 Material 2 Material 3samples Hydroxyapatite Titanium UHMWPE 28 Silicone nitride TitaniumUHMWPE 28

[0129] One Horizontal and Two Vertical Layers

[0130]FIG. 2c shows the look of a multilayer with one horizontal layerand two vertical layers.. The different material combinations used arespecified in table 4.

[0131] The best results were obtained for a pre-compacting and thenstriking the two materials. It was difficult to obtain a plastic polymerthat could bond to metal or hydroxyaptite. The samples were oftenbrittle and easily broken be hand. TABLE 4 Number of Material 1 Material2 Material 3 samples Hydroxyapatite Titanium UHMWPE 5 TitaniumHydroxyapatite UHMWPE 5 Hydroxyapatite Co-28Cr-6Mo UHMWPE 1

[0132] Two Vertical Layers

[0133]FIG. 4 shows the look of a two horizontal layer. The differentmaterial combinations used are specified in table 5.

[0134] Pre-compacting the two materials together with the machine andthen strike with the highest allowable impact energy gave the bestresult. The samples obtained were solid and did not fall apart TABLE 5Number of Material 1 Material 2 samples Co-28Cr-6Mo UHMWPE 3

[0135] Two Horizontal Layers and Two Vertical Layers

[0136]FIG. 2e shows the look of a two horizontal layer. The differentmaterial combinations used are specified in table 6.

[0137] The samples fell apart. It was difficult to melt the PMMA andUHMWPE together using these impact energy levels. The titanium layer wassolid but did not bond to the other materials. TABLE 6 Number ofMaterial 1 Material 2 Material 3 Material 4 samples Hydroxyapatite PMMAUHMWPE Titanium 8

[0138] Four Vertical Layers

[0139]FIG. 2f shows the look of a two horizontal layer. The differentmaterial combinations used are specified in table 7.

[0140] The second layer containing two vertical layers was twisted 180degrees to obtain a cross in the centre of the multilayer.

[0141] The titanium get solidified but the polymer did not phase changescompletely and the different materials could not be successfully bondedto each other.

[0142] Hydroxyapatite obtained finest samples when it was compactedtogether with titanium by first only hand compact or pre-compact withthe machine the first two vertical layers and then strike the two othervertical layers. No solid samples were obtained compressinghydroxyapatite compressed together with UHMWPE. The hydroxyapatitefelled apart and the polymer did not phase change. TABLE 8 Number ofMaterial 1 Material 2 samples Titanium UHMWPE 3 Titanium Hydroxyapatite5 Hydroxyapatite UHMWPE 5

[0143] This was a screening test for compressing multi layers. Thedensities that could be measured with scale and micrometers wereconsidered very approximately, therefore has no diagrams over densitiesbeen presented.

[0144] Due to machine and tool limitations could not all planned testsbe performed. When the material was struck before adding the second orthird material the tool parts got swollen and were sometimes impossibleto remove from the tool, which meant that the tests could not befinished.

[0145] To obtain a bonding between solid layers it was concluded thatthe first layer has only to be pre-compacted by hand or by the machine.The reason is probably that pre-compacted the material still has a highporosity where the powder particles from the two or three layers canbind to each other.

[0146] If the material is nearly completely solid with a relativedensity around 90 -95% is it difficult to bind the material together.The solidified material has taken up possible energy and is not able tobind to another material.

[0147] The ideal could be to strike one material and then add a thinlayer of powder which only is pre-compacted and the add the third layerwhich is completely solidified. The material in the centre can then bindthe two solid layers together.

[0148] All multilayer containing a polymer material, UHMWPE or PMMA, wasdifficult to obtain a bonding at low energy levels. The polymer had meltand get plastic before it can adhere to another material.

[0149] Post-processing for a multilayer is complicated, because of thedifferent material properties between the components. A polymer can forexample not be sintered and the sintering parameters between differentmetals or between a metal and a ceramic material are very different. Onesolution could be to compress one layer and then remove the material andsinter the sample. After the sintering is the material placed in thetool and next sample or powder is added and compressed. This compressingprocess can also compress or deform solid samples which means that alllayers in a multilayer could be compressed and sintered and thencompressed to one solid material body.

[0150] The samples has only been visually studied and it is thereforedifficult to conclude if there is a mechanical or chemical bondingbetween the layers in the solid samples.

[0151] To obtain a real chemical bonding between the layers and arelative density near 100% for the complete multilayer the processshould probably be performed in vacuum. If a included component is aceramic materials the powder should be pre-heated before thecompressing.

Example 2 Di-Layer of Stainless Steel and 316L-Rubber

[0152] These di-layer samples consist of one layer of ss 316L andanother layer of rubber above the ss 316L. Earlier tests with each ofthe material types separated have shown that solid samples have beenobtained with a high relative density. In this study the main object tois to investigate if a chemical bonding occurs between the two layersand how the stroke sequence should be performed to obtain the bestbonding between the material types. Applications are not well developedtoday, but with this new manufacturing process applications within thee.g. car industry, where both metal and rubber are present, could be onepossible application area.

[0153] If desired material properties would be obtained directly afterthis manufacturing process a following post-processing could be avoided.That would partly cut down the total process cost and partly avoid noenvironmental additives to the rubber. If a further post-processing isneeded manufacturing steps could be cut comparing with conventionalmanufacturing methods.

[0154] The ss 316L powder was prepared by dry mixing for 10 minutes toobtain a homogeneous particle size distribution. The rubber powder wasnot prepared partly due to that the particles would glue together andpartly that the particle size was homogeneous.

[0155] Five samples were totally produced. For all samples, ss 316L wasfirst poured into the moulding die. Different types of compactingfollowed before the rubber powder was poured into the moulding die abovethe ss 316L. An impact stroke followed, always with a certain impactenergy. This impact energy was determined by earlier tests. The strokewas stricken with an impact energy corresponding to maximum impactenergy in tests with pure rubber. Because of that two material typeswere present the weight of each material was half the normal weight,which means that this stroke was stricken with half the maximum impactenergy of rubber. Depending on what sample that was to be producedcompacting was different between the two layers. With the first samplethe ss 316L was compacted by hand with a rod before the rubber waspoured into the moulding die. Second sample a pre-compacting wasperformed and third sample a stroke at the lowest impact energy possible(150 Nm). The last (fifth) sample was stricken by half the maximumimpact energy of the earlier test with pure ss 316L. The forth samplewas stricken by an impact energy in between the impact energy of thethird and the fifth sample.

[0156] After each sample had been manufactured all tool parts weredismounted and the sample was released. The diameter and thickness weremeasured with electronic micrometers which rendered the volume of thebody. Thereafter, the weight was established with a digital scale. Allinput values from micrometers and scale were recorded automatically andstored in separate documents. Out of these results the density 1 wasobtained by taking the weight divided by the volume.

[0157] To be able to continue with the next sample, the tool needed tobe cleaned with acetone to get rid of the material rests on the tool.

[0158] To easier establish the state of a manufactured sample threevisibility index were used. Visibility index 1 corresponds to a powdersample, visibility index 2 corresponds to a brittle sample andvisibility index 3 corresponds to a solid sample.

[0159] The theoretical density was taken from the manufacturers. Out ofthat a theoretical density has been calculated that corresponds to thiscertain mix between 50% rubber and 50% ss 316L. The relative density isobtained by taking the obtained density for each sample divided by thetheoretical density.

[0160] No density 2 was measured on multilayer samples due to that insome cases (not this material combination) there were samples wherepieces were lost. In those cases the theoretical density is hard todetermine.

[0161] The dimensions of the manufactured sample in these tests is adisc with a diameter of ˜30.0 mm and a height between 5-10 mm. Theheight depends on the obtained relative density. If a relative densityof 100% should be obtained the thickness is 5.00 mm for ss 316L rubber.That is the reason to the half weight of each material type.

[0162] Powder properties are given in Table 9 and test results in Table10. TABLE 9 Properties Rubber ss316L  1. Particle size (micron) ˜496 < 2. Particle distribution 99.8 wt % < 1.0 mm 0.0% > 150 mic

42.7% < 115 mic

 3. Particle morphology Irregular Irregular  4. Powder productionPolymerised thereafter Water atom grinding to powder  5. Type ofmaterial Elastomer I

 6. Theoretical density 0.99 7.90 gc

 7. Apparent density — 2.64 gc

 8. Melt temperature (° C.) Not applicable I

 9. Sintering — 1315   temperature (° C.) 10. Hardness 40 shore A160-190 HV

[0163] TABLE 10 Sample weight (g) 15.8 Number of samples made 5 Numberof stroke sequences per sample 2 Minimum impact energy of the firststroke (Nm) 150 Maximum impact energy of the first stroke (Nm) 2000Impact energy of the second stroke (Nm) 1050 Relative density 2 of firstobtained body (%) 96.0 Maximum relative density 2 (%) 98.4 Impact energyof the first stroke at maximum 2000 relative density 2 (Nm)

[0164]FIGS. 3 and 4 show relative density as a function of impact energyper mass and of total impact energy.. The following described phenomenacould be seen for all curves.

[0165] All samples had visibility index 3.

[0166] What can be seen is that the two first samples, where the firstmaterial type is either hand compacted or pre-compacted by the machine,render a higher relative density than the third sample, where the firstmaterial type is stricken with the lowest impact energy. When the impactenergy of the first stroke increases the relative density increases andends up at a higher relative density than the two first samples. Themaximum relative density, 98.4%, is obtained when the first stroke isstruck with the highest impact energy.

[0167] The samples were all intact, but the volume was difficult toestablish because the rubber part of the samples were elastic. But thess 316L part stabilised it compared to pure rubber and density 1 showswell an indication of the obtained relative density.

[0168] Discussion:

[0169] 1.ss 316L

[0170] ss 316L has a melting temperature of 1427° C. Even though it isquite high the ss 316L part of the samples got dense. The local increaseof temperature among the particles, due to transmitted energy, makes theparticles to soften, deform and the surface of the particles to melt.This inter-particular melting enables the particles to re-solidifytogether and dense material can be obtained.

[0171] Furthermore, the ss 316L powder is softer than e.g. CoCrMo. Thehardness of ss 316L is ˜160-190 HV and CoCrMo ˜460-830 HV. The softer amaterial is the more soften and deformed the particles get. That enablesthe particles to get well soften, deformed and compressed before theinter particular melting occurs.

[0172] A pre-treating process to increase the relative density of the ss316L could be to pre-heat either only the powder or both powder and thetool. The material could possibly be heated to ˜250° C. in in airwithout any reactions of the powder occur.

[0173] Other critical parameters, that could effect the compressingresult, besides the already mentioned, melting temperature and hardness,could be the particle size, particle size distribution and particlemorphology. According to earlier tests' that were performed in Phase 1,better results were obtained with an irregular particle morphology, thanspherical morphology. Inter-particular melting occurred when irregularparticles were tested, but less when spherical particles were tested.When irregular particles get in contact with each other, due to thatthey are pressed together, the contact surface is much larger comparingwith spherical particles. The big contact area could possibly enable theparticles to easier fuse during the process and, with this theory, lessimpact energy is needed to be transmitted to the powder.

[0174] With big particles more space is present between the particlesthan with small particles. That makes it harder to obtain a dense andwell compressed sample. The advantage with big particles, compared withsmall particles, is that the total surface of bigger particles is lessthan with small particles. A large total surface makes the surfaceenergy high, and correspondingly higher impact energy could be requiredto reach desired results. On the other hand, small particles couldpossibly reach a higher compressed rate because the space between theparticles is smaller than between large particles. The optimal particlesize is still a question that needs to be answered.

[0175] The particle size distribution should probably be wide. Smallparticles could fill up the empty space between big particles.

[0176] It is important to obtain samples with less than 5% pores becausethe pores ate with that closed in the material. If there are more than5% pores canals in the material, humidity can get into the canals of thematerial. That results in corrosion of the material, and the propertiesof the manufactured sample are low. If there are more than 5% pores thesamples must be sintered to eliminate the canals and pores of thematerial.

[0177] To obtain a total dense sample, i.e. 99-100%, the atmospheremight need to be different from the present used in this test. If air isincluded in the material, the density decreases. To obtain a densematerial, vacuum could be an alternative.

[0178] One alternative could be to sinter the ss 316L part first.Thereafter could the ss 316L part be put in the moulding die again andthe rubber could be added above the ss 316L. It seems to that rubberbonded to ss 316L in this test and therefore it could be possible thatrubber would bond to the sintered ss 316L as well. In that case thesample, at least the metal part, has probably reached the desiredproperties though the metal part has been sintered.

[0179] Rubber

[0180] The hardness of materials affect the results. The hardness ofrubber is lower comparing with e.g. PMMA. PMMA required a higher amountof transformed impact energy compared with rubber to obtain a samplewith visibility index 2. The softer a material is the more soften anddeformed the particles get, which easily has occurred with the rubberparticles. That enables the particles to get softened, deformed andcompressed before the inter-particular melting occurs.

[0181] The particles could still be determined in the sample. Thereforeshould probably a post-processing follows. The rubber normally processesas a thermoplastic polymer where vulcanising follows. The vulcanisingrenders a high elastic material, elastomer, due to that the materialgets cross-linked.

[0182] There exists hitherto no corresponding powder metallurgy forpolymers and therefore it could be difficult to find what and how theparameters should be changed. But probably could some of the discussionbe valid to polymers as well. Other critical parameters, that couldeffect the compressing result, besides the already mentioned, meltingtemperature, could be the particle size, particle size distribution andparticle morphology. When irregular particles get in contact with eachother, due to that they are pressed together, the contact surface ismuch larger comparing with spherical particles. The big contact areacould possibly enable the particles to easier fuse during the processand, with this theory, less impact energy is needed to be transmitted tothe powder.

[0183] If big particles are used more space is present between theparticles than with small particles. That makes it harder to obtain adense and well compressed sample. The advantage with big particles,compared with small particles, is that the total surface of biggerparticles is less than with small particles. A large total surface makesthe surface energy high and correspondingly higher impact energy couldbe required to reach desired results. On the other hand, small particlescould possibly reach a higher compressed rate because the space betweenthe particles is smaller than between large particles. The optimalparticle size is still a question that needs to be answered.

[0184] The particle size distribution should probably be wide. Whendifferent particle sizes are used small particles could fill up theempty space between big particles. Thus there are particle surfaces thatare in contact with other particles everywhere in the sample. Thatincreases the possibility to succeed in inter-particular melting (e.g.small particles' surfaces against big particles' surfaces).

[0185] Rubber is an amorphous polymer. In this fast manufacturingprocess the sample is already room tempered when it is released from themould. That means that the cooling process is much faster than othermanufacturing processes. Due to this fast cooling process thismanufacturing process could perhaps suit amorphous polymer productionbetter than crystalline polymer production. The structure of crystallinepolymers is in the form of lamellas and amorphous polymers' structure isnot a well organised structure. To obtain this organised structure ofcrystalline polymers the cooling time could probably need more time thanfor amorphous polymers. This cooling process could possibly effect thestructure and material properties of the rubber. Therefore is there animportance of investigating the microstructure and the materialproperties.

[0186] Layer

[0187] Between these two material types there is some kind of bonding.Exactly how these material types are bound together will be shown in themicrostructure test. How will the highest relative density be obtainedof both material, and in the mean time obtain a chemical bonding betweenthe material types? As can be seen in the figures the relative densityis higher when the first material type is compacted, not stricken withlow impact energy. ss 316L and rubber particles can possibly get incontact with each other if the surface is somewhat rough compared withthe samples where the a low impact energy is transformed to the powder.When particles can be in contact before the stroke process they can bemore packed, and more integrated.

[0188] But if the impact energy of the first stroke increases therelative density increases as well. That could be that rubber could bindto a “polished” surface where a stroke has been performed due to thesoftness of rubber. Rubber could possibly act as glue on the ss 316Lsurface.

[0189] The invention concerns a new method which comprises bothpre-compacting and in some cases post-compacting and there between atleast one stroke on the material. The new method has proved to give verygood results and is an improved process over the prior art.

[0190] The invention is not limited to the above described embodimentsand examples. It is an advantage that-the present process does notrequire the use of additives.

[0191] However, it is possible that the use of additives could proveadvantageous in some embodiments. Likewise, it is usually not necessaryto use vacuum or an inert gas to prevent oxidation of the material bodybeing compressed. However, some materials may require vacuum or an inertgas to produce a body of extreme purity or high density. Thus, althoughthe use of additives, vacuum and inert gas are not required according tothe invention the use thereof is not excluded. Other modifications ofthe method and product of the invention may also be possible within thescope of the following claims.

1. A method of producing a multilayer body by coalescence, characterisedin that the method comprises the steps of a) filling a pre-compactingmould with a start material in the form of powder, pellets, grains andthe like, b) pre-compacting the material at least once and c)compressing the material in a compression mould by at least one stroke,where a striking unit emits enough kinetic energy to form the body whenstriking the material inserted in the compression mould, causingcoalescence of the material, d) at least one further material beinginserted into the mould in the form of powder, pellets, grains and thelike, either in step a), after compacting in step b) or aftercompressing the start material in step c), e) if necessary, furtherpre-compacting and/or compressing being performed after the insertion ofthe at least one further material.
 2. A method according to claim 1,characterised in that the pre-compacting mould and the compressing mouldare the same mould.
 3. A method according to any of the precedingclaims, characterised in that the material is pre-compacted with apressure of at least about 0.25×10⁸ N/m², in air and at roomtemperature.
 4. A method according to claim 3, characterised in that thematerial is pre-compacted with a pressure of at least about 0.6×10⁸N/m².
 5. A method according to any of the preceding claims,characterised in that the method comprises pre-compacting the materialat least twice.
 6. A method of producing a multilayer body bycoalescence, characterised in that the method comprises compressing asolid body of a start material in a compression mould by at least onestroke, where a striking unit emits enough energy to cause coalescenceof the material in the body, at least one further material beinginserted in the mould, either in the form of powder, pellets, grains andthe like or in the form of a solid body, the at least one furthermaterial also being struck by the striking unit, either in the firststroke or in a later stroke so that the at least two materials form anintegral body.
 7. A method according to any of claims 1-5 or claim 6,characterised in that the compression strokes emit a total energycorresponding to at least 100 Nm in a cylindrical tool having a strikingarea of 7 cm²in air and at room temperature.
 8. A method according toclaim 7, characterised in that the compression strokes emit a totalenergy corresponding to at least 300 Nm in a cylindrical tool having astriking area of 7 cm².
 9. A method according to claim 8, characterisedin that the compression strokes emit a total energy corresponding to atleast 600 Nm in a cylindrical tool having a striking area of 7 cm². 10.A method according to claim 9, characterised in that the compressionstrokes emit a total energy corresponding to at least 1000 Nm in acylindrical tool having a striking area of 7 cm².
 11. A method accordingto claim 10, characterised in that the compression strokes emit a totalenergy corresponding to at least 2000 Nm in a cylindrical tool having astriking area of 7 cm².
 12. A method according to any of claim 1-5 orclaim 6, characterised in that the compression strokes emit an energyper mass corresponding to at least 5 Nm/g in a cylindrical tool having astriking area of 7 cm² in air and at room temperature.
 13. A methodaccording to claim 12, characterised in that the compression strokesemit an energy per mass corresponding to at least 20 Nm/g in acylindrical tool having a striking area of 7 cm².
 14. A method accordingto claim 13, characterised in that the compression strokes emit anenergy per mass corresponding to at least 100 Nm/g in a cylindrical toolhaving a striking area of 7 cm².
 15. A method according to claim 14,characterised in that the compression strokes emit an energy per masscorresponding to at least 250 Nm/g in a cylindrical tool having astriking area of 7 cm².
 16. A method according to claim 15,characterised in that the compression strokes emit an energy per masscorresponding to at least 350 Nm/g in a cylindrical tool having astriking area of 7 cm².
 17. A method according to any of the precedingclaims, characterised in that the multilayer body is compressed to arelative density of at least 60%, preferably 65%.
 18. A method accordingto claim 17, characterised in that the multilayer body is compressed toa relative density of at least 70%, preferably 75%.
 19. A methodaccording to claim 18, characterised in that the multilayer body iscompressed to a relative-density of at least 80%, preferably at least85% and especially at least 90% up to 100%.
 20. A method according toany of the preceding claims, characterised in that the method comprisesa step of post-compacting the body at least once after the compressionstep.
 21. A method according to any of the preceding claims,characterised in that the materials in the multilayer body are chosenfrom the group comprising metallic, ceramic and polymeric materials..22. A method according to claim 21, characterised in that one of thematerials in the multilayer body contains a reinforcing phase which ischosen from the group comprising carbon, glass, metal, polymeric andceramic material.
 23. A method according to claim 21, characterised inthat the multilayer materials are chosen from the group comprisingUHMWPE, PMMA, nitrile rubber, aluminium alloys and titanium.
 24. Amethod according to any of the preceding claims, characterised in thatthe body produced is a medical implant, such as a skeletal or toothprosthesis.
 25. A method according to any of the preceding claims,characterised in that the method comprises a step of post-heating and/orsintering the body any time after the compression or thepost-compacting.
 26. A method according to any of the preceding claims,characterised in that the body produced is a green body.
 27. A method ofproducing a body according to claim 27, characterised in that the methodalso comprises a further step of sintering the green body.
 28. A methodaccording to any of the preceding claims, characterised in that thematerials are a medically acceptable materials.
 29. A method accordingto any of the preceding claims, characterised in that the at least oneof the materials comprises a lubricant and/or a sintering aid.
 30. Amethod according to claim 6, characterised in that the method alsocomprises deforming the body.
 31. A product obtained by the methodaccording to any of claims 1-30.
 32. A product according to claim 31,characterised in being a medical device or instrument.
 33. A productaccording to claim 31, characterised in being a non medical device.